It is known to detect various internal states such as excess and deficiency of hydrogen, excess and deficiency of oxygen and a degree of wetness of an electrolyte membrane in a fuel cell. For example, to detect excess and deficiency of hydrogen, it is known to use a reaction resistance value of a hydrogen electrode (anode electrode) as an index of this detection. Further, to detect a wet/dry state of the electrolyte membrane, a state quantity such as an electrolyte membrane resistance value or an ionomer resistance value may be used as an index.
In estimating/calculating the above state quantity, it is known to measure and use an impedance value.
For example, in JP2013-258042, it is proposed to calculate an ionomer resistance value on the basis of an equation supposed in advance from an imaginary part of a measured impedance and use this ionomer resistance value as an index for the detection of a wet/dry state of a fuel cell.